As set out in the above referenced applications/patents, the Applicant has spent a substantial amount of time and effort in developing printheads that incorporate micro electromechanical system (MEMS)—based components to achieve the ejection of ink necessary for printing.
As a result of the Applicant's research and development, the Applicant has been able to develop printheads having one or more printhead chips that together incorporate up to 84 000 nozzle arrangements. The Applicant has also developed suitable processor technology that is capable of controlling operation of such printheads. In particular, the processor technology and the printheads are capable of cooperating to generate resolutions of 1600 dpi and higher in some cases. Examples of suitable processor technology are provided in the above referenced patent applications/patents.
The Applicant has overcome substantial difficulties in achieving the necessary ink flow and ink drop separation within the ink jet printheads.
Each of the nozzle arrangements of the printhead chip incorporates one or more moving components in order to achieve drop ejection. The moving components are provided in a number of various configurations.
Generally, each nozzle arrangement has a structure that at least partially defines a nozzle chamber. This structure can be active or static.
When the structure is active, the structure moves relative to a chip substrate to eject ink from an ink ejection port defined by the structure. In this configuration, the structure can define just a roof for the nozzle chamber or can define both the roof and sidewalls of the nozzle chamber. Further, in this configuration, a static ink ejection formation is provided. The active structure moves relative to this formation to reduce a volume of the nozzle chamber in order to achieve the necessary build up of ink pressure. The static formation can simply be walls defined by the substrate. In this case, the active structure is usually in the form of a roof that is displaceable into and out of the nozzle chamber to achieve the ejection of ink from the ink ejection port.
Instead, the static formation can extend into the nozzle chamber to define an ink ejection area that faces a direction of ink drop ejection. The active structure then includes sidewalls that move relative to the static formation when the active structure is displaced to eject ink.
It will be appreciated that some form of seal is required between the active structure and the static formation to inhibit ink from escaping from the nozzle chamber when the active structure is displaced towards the substrate and ink pressure is developed in the nozzle chamber.
When the structure defining the nozzle chamber is static, an ink ejection member is usually positioned in the nozzle chamber. The structure also has a roof with an ink ejection port defined in the roof. The ink ejection member is often connected to an actuator that extends through a wall of the structure. The ink ejection member is actuated by the actuator to be displaceable towards and away from the roof to eject ink from the ink ejection port.
It will be appreciated that a seal is required at a juncture between the actuator or ink ejection member and the wall.
Applicant has found that it is convenient to use a surface tension of the ink to set up a fluidic seal between the active and static components of the nozzle arrangements. The fluidic seal uses surface tension of the ink to set up a meniscus between the active and static components so that the meniscus can act as a suitable seal to inhibit the leakage of ink.
Cohesive forces between liquid molecules are responsible for the phenomenon known as surface tension. The molecules at the surface do not have other like molecules on all sides of them and consequently they cohere more strongly to those directly associated with them on the surface. This forms a surface “film” which makes it more difficult to move an object through the surface than to move it when it is completely submersed.
Surface tension is typically measured in dynes/cm, the force in dynes required to break a film of length 1 cm. Equivalently, it can be stated as surface energy in ergs per square centimeter. Water at 20° C. has a surface tension of 72.8 dynes/cm compared to 22.3 for ethyl alcohol and 465 for mercury.
As is also known, a liquid can also experience adhesive forces when the molecules adhere to a material other than the liquid. This causes such phenomena as capillary action.
Applicant has found that an effective fluidic seal can be achieved by utilizing the phenomena of surface tension and adhesion.
A particular difficulty that the Applicant has discovered and addressed in achieving such a fluidic seal is the problem associated with excessive adhesion or “wetting” when a meniscus is stretched to accommodate relative movement of the active and static components. In particular, wetting occurs when the relative movement overcomes surface tension and an edge of the meniscus moves across a surface, to which the meniscus is adhered. This results in a weakening of the meniscus due to the larger area of the meniscus and increases the likelihood of failure of the meniscus and subsequent leaking of ink.
The Applicant has conceived this invention in order to address these difficulties. Furthermore, the Applicant has obtained surprisingly effective fluidic seals when addressing these difficulties by developing sealing structures that support such fluidic seals.